1. Field of the Invention
This invention is related to feeler-type mechanical calipers for measuring and recording irregularities in the inner wall of well flow conductors. More particularly, the invention relates to TFL calipers.
2. Prior Art
Calipers have been used for many years as part of an overall effort at detecting and controlling corrosion in oilfield pipe, including both tubing and casing. There are several mechanical and electronic types of calipers available that accomplish the task of determining imperfections in pipe. Some have very specific limitations in their application. For example, within the field of "electronic" calipers, two such devices utilize coils to sense either a magnetic field (magnetic caliper) or an eddy current phase shift between an exciter coil and a detector coil (eddy current).
The present invention is within the field of "feeler" type mechanical calipers and utilizes a plurality of feelers held within a sensing mechanism. The feelers are spring loaded and are biased against the bore wall of well flow conductors such as flow lines and well tubing to travel thereinto, and detect, pits and other imperfections in the wall. To date, these calipers have generally been confined to "wireline" operations. That is to say, the drive mechanism, recording mechanism and sensing mechanism have been housed in a single unit. This has always been the result of the inherent difficulty of centering the sensing mechanism within the tubing and because the drive mechanism was connected, directly through a drive shaft, to the recording mechanism making it extremely difficult to separate the caliper into individual units. Of course, to be useful in TFL operations, the entire mechanism must be articulated for passage through a severe bend in the flow conductor for vertical entry into the tubing from a horizontal flow line. A standard, long-ago adopted by the industry, requires that the radius of such bends be no less than a 5 foot radius.
Pertinent patents in this field include the Chaney et al U.S. Pat. No. 2,518,663 which discloses and claims a caliper having a sensing section having a housing and a plurality of independently movable feelers spaced circumferentially of said housing and adapted for independent lateral movement between the housing and the tube wall being calipered. Other important features claimed therein have been widely used in the industry since issuance of the patent.
A subsequent Chaney et al U.S. Pat. No. 2,879,604, taught that it was possible to individually record the lateral movement of individual feeler arms in the sensing section of the caliper. To utilize this device, however, it was necessary to use electrical line to lower and retrieve the caliper in the well. The feeler arm mechanism, however, was essentially that claimed previously in the No. '663 patent.
Another Chaney et al Patent in this field is U.S. Pat. No. 2,567,548, which claims a caliper having a rotative and axially movable chart for recording deviations in the inside diameter of a pipe.